Semiconductor component and method of manufacture

ABSTRACT

A semiconductor component comprises a substrate (101), a two flexible pressure sensor diaphragms (106, 303) supported by the substrate (101), and a fixed electrode (203) between the two diaphragms (106, 303). The two diaphragms (106, 303) and the fixed electrode (203) are electrodes of two differential capacitors. The substrate (101) has a hole (601) extending from one surface (107) of the substrate (101) to an opposite surface (108) of the substrate (101). The hole (601) is located underneath the two diaphragms (106, 303), and the hole (601) at the opposite surfaces (107, 108) of the substrate (101) is preferably larger than the hole (601) at an interior portion of the substrate (101).

BACKGROUND OF THE INVENTION

This invention relates, in general, to electronic components, and moreparticularly, to semiconductor components.

Differential capacitive pressure sensors typically have a fixedelectrode, a single pressure-movable diaphragm electrode, and a smallgap separating the two electrodes wherein the gap is exposed to thepressure sensing environment. During sensor operation, a change inpressure deflects the diaphragm electrode and modifies the size of thegap between the two electrodes, which changes the capacitance measuredbetween the two electrodes.

However, these capacitive pressure sensors are highly susceptible toparticulate contamination because dust and other particulates can easilybecome trapped in the gap. The particulates come from ambient duringsensor fabrication, assembly, and from the gas or liquid pressuresensing media during sensor operation. The particulates prevent thediaphragm electrode from moving properly in response to changes inpressure.

Furthermore, when the pressure sensing environment is ambient, the priorart capacitive pressure sensors are also susceptible to humidity andother forms of moisture in the ambient because the moisture changes thedielectric constant of the air between the two electrodes. Therefore,humidity variations change the capacitance measured by the sensor evenwhen the ambient pressure remains constant.

Moreover, some differential capacitive pressure sensors also requirelarge support substrates that waste space and increase the cost of thesensors.

Accordingly, a need exists for smaller and cost-effective pressuresensors that are not susceptible to particulates or moisture from thepressure sensing environments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 through 8 illustrate cross-sectional views of an embodiment ofan electronic component after different stages of fabrication inaccordance with the present invention.

For simplicity and clarity of illustration, elements in the drawings arenot necessarily drawn to scale. Furthermore, the same reference numeralsin different figures denote the same elements.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of an electronic component 100 afterseveral initial manufacturing steps. Component 100 includes a substrate101 having a bottom surface 107 and a top surface 108 opposite surface107. Substrate 101 is used to support a sealed composite hollowdiaphragm or a capacitive pressure sensor diaphragm, as explainedhereinafter. Substrate 101 can be comprised of a semiconductor materialsuch as silicon, germanium, gallium arsenide, or the like. However, inthe preferred embodiment, substrate 101 comprises a silicon substratehaving a single-crystalline structure for reasons explained hereinafter.

Isolation and etch stop layers 102 and 103 are sequentially disposedover surface 108 of substrate 101 using, for example, thermal growth,vapor deposition, or other similar techniques. Layers 102 and 103provide electric and parasitic isolation between substrate 101 and thesealed hollow composite diaphragm (explained hereinafter) formed oversubstrate 101. Therefore, the use of layers 102 and 103 enables anintegrated circuit to be formed in substrate 101 to provide on-chippressure measurements and calculations. Layers 102 and 103 also serve asetch stops during a subsequent etching of substrate 101, describedhereinafter. In the preferred embodiment, layer 102 comprisesapproximately one to three micrometers of a dielectric such as siliconoxide, and layer 103 comprises less than approximately half of amicrometer of a different dielectric such as silicon nitride.

Next a hole is formed into layers 102 and 103 using wet or dry etchingtechniques. The hole can be approximately one hundred to one thousandmicrometers wide. Then, a hole-widening layer 104 is disposed into thehole and over surface 108 of substrate 101 using, for example, a vapordeposition technique. Layer 104 enables a wider hole to be etched intosubstrate 101, as described hereinafter. Layer 104 preferably comprisesa material that is isotropically etchable by the same etchant thatanisotropically etches substrate 101. In the preferred embodiment, layer104 comprises approximately one and a half to three and a halfmicrometers of silicon having a polycrystalline structure, known in theart as polysilicon. A planarizing technique, such as chemical-mechanicalpolishing, can be used to flatten the top surface of the semiconductorstructure after the deposition of layer 104.

Then, an etch stop 105 is disposed over layers 103 and 104. In thepreferred embodiment, etch stop 105 comprises less than approximatelyhalf of a micrometer of a dielectric such as silicon nitride.Subsequently, a diaphragm 106 is disposed overlying etch stop 105.Diaphragm 106 serves as a bottom diaphragm of the sealed compositehollow diaphragm and also serves as the bottom electrode of thedifferential pressure sensing portion of component 100. In the preferredembodiment, diaphragm 106 is formed by depositing and then patterningapproximately one to three micrometers of an electrically conductivematerial such as doped polysilicon.

FIG. 2 illustrates component 100 after several additional manufacturingsteps. An isolation layer 201 is deposited over diaphragm 106 and etchstop 105. Layer 201 is patterned with holes to expose portions ofdiaphragm 106. Layer 201 electrical isolates diaphragm 106 from anoverlying fixed electrode (described hereinafter). In the preferredembodiment, layer 201 comprises less than approximately half of amicrometer of a dielectric such as silicon nitride.

After the patterning of layer 201, a sacrificial layer 202 is depositedand patterned over diaphragm 106 and layer 201. Layer 202 is formed inand over the holes of layer 201 to directly or physically contactdiaphragm 106. The subsequent complete removal of layer 202 enablesdiaphragm 106 to be movable independent of a fixed electrode (describedhereinafter). Layer 202 preferably comprises a material that can be wetetched selectively over layer 201 and diaphragm 106. In the preferredembodiment, layer 202 comprises approximately one to three micrometersof a dielectric such as silicon oxide, phosphosilicate glass, or thelike.

A fixed electrode 203 is formed overlying diaphragm 106 and layers 201and 202. Fixed electrode 203 serves as a central immobile electrode forthe differential pressure sensing portion of component 100. Electrode203 is electrically isolated from diaphragm 106 by isolation layer 201.Electrode 203 is patterned with a set or plurality of holes to exposeportions of sacrificial layer 202. The holes of electrode 203 arealigned over different regions of isolation layer 201 and preferably donot overlie the holes of isolation layer 201. In the preferredembodiment, electrode 203 comprises approximately one to threemicrometers of a similar material used for diaphragm 106, and the holesof electrode 203 are each approximately two to ten micrometers wide.

FIG. 3 illustrates component 100 after subsequent processing. Anisolation layer 301 is disposed over fixed electrode 203 and isolationlayer 201. Layer 301 electrically isolates fixed electrode 203 from asubsequently formed diaphragm electrode (explained hereinafter). Layer301 is patterned with an opening to expose the holes of fixed electrode203. In an alternative embodiment, layer 301 is patterned with separateopenings for each of the holes of fixed electrode 203. In the preferredembodiment, layer 301 comprises less than approximately half of amicrometer of a similar material used for layer 201.

Next, a sacrificial layer 302 is deposited over layer 301, over fixedelectrode 203, in the opening of layer 301, and in the holes of fixedelectrode 203 to physically contact sacrificial layer 202. Thesubsequent complete removal of layer 302 enables a subsequently formeddiaphragm (explained hereinafter) to be movable independent of fixedelectrode 203. In the preferred embodiment, sacrificial layer 302comprises approximately one to three micrometers of a similar materialused for sacrificial layer 202 so that layer 302 can be removed with thesame etchant as layer 202 without substantially etching layers 201 and301, diaphragm 106, or electrode 203.

A first etch mask (not shown) is formed over layers 302 and 301 todefine the outer perimeter of layer 302. After an etching step and theremoval of the first etch mask, a second etch mask (not shown) is formedover layers 302 and 301 before anisotropically etching a set orplurality of holes into sacrificial layers 302 and 202. The holesoverlie, fit within, and extend through the holes of fixed electrode203. Layer 201 serves as an etch stop for this anisotropic etching step.In the preferred embodiment, the holes of this etching step areapproximately two to ten micrometers wide and are concentric with theholes of fixed electrode 203.

After the removal of the second etch mask, a diaphragm 303 is formedover sacrificial layer 302, isolation layer 301, fixed electrode 203,and diaphragm 106. Diaphragm 303 serves as a top electrode for thepressure sensing portion of component 100. Diaphragm 303 is electricallyisolated from fixed electrode 203 by isolation layer 301. Diaphragm 303also has at least one hole 304 to expose a portion of sacrificial layer302. Hole 304 preferably does not overlie a central portion of layer 104for reasons explained hereinafter. Diaphragm 303 is preferably formed bydepositing and then patterning approximately two to twelve micrometersof a similar material used for diaphragm 106 and electrode 203.

The material used for diaphragm 303 is also deposited into the holes ofsacrificial layers 302 and 202 to form a plurality of support pillars,columns, beams, or posts 305 for diaphragm 303. Posts 305 are preferablyabout one to ten micrometers wide and about ten to fifty micrometersapart from each other to prevent localized deflections of diaphragms 106and 303, as explained in more detailed hereinafter. Posts 305 areelectrically isolated from diaphragm 106 by isolation layer 201.Although only two posts are portrayed in FIG. 3, it is understood thatthe specific number of posts depends upon the size of diaphragms 303 and106 wherein larger diaphragms requires more posts.

FIG. 4 illustrates component 100 after further manufacturing.Sacrificial layers 302 and 202 are removed to create a cavity 401between diaphragms 106 and 303 wherein fixed electrode 203 and posts 305remains in cavity 401. Hole 304 in diaphragm 303 permits an etchant tocontact and etch sacrificial layer 302, and the holes in fixed electrode203 permit an etchant to contact and etch sacrificial layer 202. Tosimplify the removal process, a single etchant can be used to etch bothsacrificial layers 302 and 202 while diaphragms 106 and 303, posts 305,isolation layers 201 and 301, and fixed electrode 203 remainsubstantially unaffected by the etchant. In the preferred embodiment, awet etchant comprising hydrofluoric acid, buffered hydrofluoric acid, orthe like is used to selectively etch layers 302 and 202 over diaphragms106 and 303, posts 305, isolation layers 201 and 301, and fixedelectrode 203. Although only one etch hole is portrayed in FIG. 4, it isunderstood that the specific number of etch holes depends on the size ofdiaphragms 106 and 303 wherein larger diaphragms require more etchholes.

After removing sacrificial layers 302 and 202, isolation layers 201 and301 keep fixed electrode 203 electrically isolated from and diaphragms106 and 303, respectively. The thickness of layers 302 and 202 beforetheir removal determines the final spacing between diaphragm 303 andelectrode 203 and between electrode 203 and diaphragm 106, respectively.After removing layers 302 and 202, fixed electrode 203 is preferably notsupported by the inner surfaces or walls of cavity 401. Instead,electrode 203 is preferably more securely supported by isolation layer201, diaphragm 106, and substrate 101.

Following the formation of cavity 401, an anti-stiction process can beperformed to prevent the stiction of fixed electrode with diaphragms 106and 303 during the operation of component 100. The anti-stictionprocesses or structures can include, for example, stand-offs, dimples,freeze-drying techniques, supercritical carbon dioxide drying, oranti-stiction coatings.

FIG. 5 illustrates component 100 after further manufacturing steps. Acavity sealing layer 501 is deposited over diaphragm 303, over isolationlayer 301, and in hole 304. Layer 501 seals cavity 401 and preventscavity 401 and fixed electrode 203 from being exposed to ambient. In thepreferred embodiment, layer 501 comprises about a half to fourmicrometers of silicon oxide. Also in the preferred embodiment, thepressure in cavity 401 is approximately thirty milli-Torr to one Torr,which can be achieved by drawing the deposition chamber to approximatelythirty milli-Torr to one Torr before and during the deposition of layer501.

Next, a first contact hole is sequentially etched into layers 501, 301,and 201 to permit the formation of electrical contact 502. A secondcontact hole is also etched into layer 501 to permit the formation ofelectrical contact 503. A third contact hole is sequentially etched intolayers 501 and 301 to permit the formation of electrical contact 504.One, two, or three separate etch masks may be used to etch the threecontact holes. In the preferred embodiment, electrical contacts 502,503, and 504 comprise materials that are used for source and draincontacts in conventional metal-oxide-semiconductor field-effecttransistors. As an example, contacts 502, 503, and 504 can comprisealuminum silicon.

A first protection layer or etch mask 505 is formed over surface 108 ofsubstrate 101, cavity sealing layer 501, electrical contacts 502, 503,and 504, and the semiconductor structure comprising diaphragms 106 and303 and fixed electrode 203. Etch mask 505 is devoid of any openings orholes and continuously covers substantially all of surface 108. A secondprotection layer or etch mask 506 is formed over surface 107 ofsubstrate 101. Etch mask 506 has an opening directly underlyinghole-widening layer 104 and exposes a portion of substrate 101 alongsurface 107. Substrate 101 can be thinned from surface 107 beforedepositing etch mask 506 over surface 107. In the preferred embodiment,etch masks 505 and 506 comprise approximately a half to two micrometersof silicon nitride.

FIGS. 6 and 7 illustrate component 100 during a subsequent etching step.After the formation of etch masks 505 and 506, a cavity or hole 601 isetched into substrate 101 beginning from the exposed portion of surface107. In the preferred embodiment, an anisotropic wet etchant 602 such aspotassium hydroxide or tetra-methyl-ammonium hydroxide is used to etchhole 601 into substrate 101. In this preferred embodiment, substrate 101will be etched along the <100> crystal plane, and the sidewalls of hole601 will form a 54.7 degree angle with surface 107 of substrate 101.

As hole 601 reaches cavity-widening layer 104 in the preferredembodiment, etchant 602 will isotropically etch layer 104. Because ofthe isotropic etching of layer 104, a portion of surface 108 will beexposed to etchant 602, as portrayed in FIG. 6. Additionally, as thisportion of surface 108 is exposed to etchant 602, etchant 602 willanisotropically etch substrate 101 along the <100> crystal plane fromsurface 108, as portrayed in FIG. 7. Eventually, all of layer 104 isremoved by etchant 602, and the size of hole 601 is widened at surface108.

In this etching step, etch masks 505 and 506, layers 102 and 103, andetch stop 105 are preferably all etch-resistant to etchant 602. Etchmask 505 prevents etchant 602 from directly etching layer 104 andsurface 108 of substrate 101. Instead, etchant 602 is supplied to layer104 and surface 108 only through hole 601 from surface 107 of substrate101.

This preferred etching embodiment of FIGS. 6 and 7 reduces the size ofcomponent 100 because the portions of hole 601 at surfaces 107 and 108of substrate 101 are larger or wider than other portions of hole 601 atinner, interior, middle, or central portions of substrate 101. Toachieve the smallest component 100, the opening in etch mask 506 ispreferably approximately the same size as hole-widening layer 104.

In an alternative embodiment, a dry etching technique or other bulkmicromachining techniques can be used in place of or in combination withthe aforementioned wet etching technique. As an example, a dry etchantcan be used to initially etch hole 601 from surface 107 to a pointwithin substrate 101. Next, a second etchant can be used to etch furtherinto substrate 101, to remove layer 104 and expose a portion of surface108 of substrate 101, and to isotropically etch the remaining portion ofhole 601.

Next, FIG. 8 illustrates component 100 after several additionalmanufacturing steps. Etch mask 505 is removed to expose electricalcontacts 502, 503, and 504. In the preferred embodiment, a portion ofetch stop 105 directly above hole 601 is removed. Also in the preferredembodiment, most of cavity sealing layer 501 is removed, but a smallportion of layer 501 remains in hole 304 of diaphragm 303 to keep cavity401 sealed. Alternatively, only a portion of cavity sealing layer 501directly above hole 601 is removed. With the aforementioned removal oflayer 501, etch mask 505 and etch stop 105, portions of diaphragms 303and 106 located directly above hole 601 are flexible or movable relativeto substrate 101 and in a direction substantially perpendicular tosurfaces 107 and 108 of substrate 101. Fixed electrode 203 remainsimmovable or stationary relative to substrate 101.

In an alternative embodiment, cavity sealing layer 501 is not etched orremoved, and the portion of etch stop 105 directly above hole 601 isalso not removed. This alternative embodiment provides electricalisolation of diaphragms 303 and 106 from the pressure sensingenvironment, but the flexibility of diaphragms 106 and 303 is reduced.To maintain a minimum amount of flexibility in diaphragm 303, hole 304in diaphragm 303 is preferably not located over hole 601 so that whenhole 304 is filled with cavity sealing layer 501, layer 501 does notdirectly contact or directly couple the portions of diaphragm 303 andelectrode 203 that directly overlie hole 601.

As portrayed in FIG. 8, component 100 is a differential capacitivepressure sensor. Diaphragms 303 and 106 form a differential capacitivepressure sensing element or a sealed composite hollow diaphragm thatcontains a fixed electrode 203 inside. Diaphragms 303 and 106 are twoflexible electrodes of the composite hollow diaphragm. As explained inmore detail hereinafter, the sealed composite hollow diaphragm moves inresponse to a differential pressure. The sealed composite hollowdiaphragm is supported by substrate 101 and directly overlies hole 601in substrate 101.

During operation of component 100, diaphragm 303 is exposed to a firstpressure and is isolated from a second pressure, and diaphragm 106 isexposed to the second pressure and is isolated from the first pressure.If the first pressure is greater than the second pressure, thendiaphragm 303 will move or deflect toward fixed electrode 203. Withposts 305 mechanically coupling diaphragms 303 and 106, as diaphragm 303moves towards fixed electrode 203, posts 305 move or deflect diaphragm106 away from fixed electrode 203. Posts 305 are preferably rigid orstiff to simultaneously move diaphragm 106 in a similar manner and thesame distance that diaphragm 303 moves.

If the second pressure is greater than the first pressure, thendiaphragm 106 will move toward electrode 203, and posts 305 willsimultaneously move diaphragm 303 away from electrode 203. Electrode 203will not move in response to either of the first or second pressures. Asdiaphragms 303 and 106 move toward or away from electrode 203, thecapacitance between diaphragm 303 and electrode 203 changes in onedirection, and the capacitance between diaphragm 106 and electrode 203changes in an opposite direction. This differential capacitance can bemeasured by an integrated circuit in substrate 101 or on a separatesubstrate.

In summary, an improved semiconductor differential capacitive pressuresensing component or device has a sealed composite hollow diaphragm witha fixed electrode therein to detect changes in air, gas, or liquidpressure. The pressure sensing device described herein overcomes manydisadvantages of the prior art. For example, the pressure sensing devicehas a smaller size because of the method of forming the hole within thesupport substrate. As another example, the size of the pressure sensingdevice is also reduced because the two flexible diaphragms overlap eachother and do not overlie different portions of the underlying supportsubstrate. In addition, the sealed composite hollow diaphragm eliminatesthe prior art problems of particulate contamination and moisturecondensation during the manufacturing and operation of the pressuresensing device. Furthermore, the posts that mechanically couple the twoflexible diaphragms prevent common mode pressure problems of prior artpressure sensors where two opposing flexible diaphragms may both deflecttoward a middle fixed electrode. Moreover, the cost of the pressuresensing device is reduced because the two flexible diaphragms are notindividually made from expensive materials such as sapphire. The cost isfurther reduced because the two flexible diaphragms are not assembledtogether using expensive, difficult, and inaccurate aligning techniqueswhereby the two diaphragms are bonded together with an adhesive or otherbonding agent. Additionally, the use of a capacitive sensing techniquereduces the temperature sensitivity of the pressure measurement andsignificantly increases the low pressure sensitivity compared to apiezoresistive sensing technique.

The semiconductor differential pressure sensing component describedherein can be used in a variety of applications including, but notlimited to, liquid and gas flow meters, consumer appliances such aswashing machines, heating, ventilation, and air conditioningapplications, and various automotive applications. Furthermore, theconcepts presented herein are also applicable to other pressure sensingtechniques such as tunneling tip devices, thermal detectors,piezoresistive devices, and barometric pressure sensors because thetransduction mechanism is protected from the environment in which thepressure measurement is performed.

While the invention has been particularly shown and described mainlywith reference to preferred embodiments, it will be understood by thoseskilled in the art that changes in form and detail may be made withoutdeparting from the spirit and scope of the invention. For instance, thenumerous details set forth herein such as, for example, materialcompositions and specific etchants are provided to facilitate theunderstanding of the present invention and are not provided to limit thescope of the invention.

Additionally, FIG. 8 illustrates posts 305 electrically coupled todiaphragm 303. However, in an alternative embodiment, posts 305 can beelectrically isolated from diaphragm 303 to reduce the parasiticcapacitances between posts 305 and fixed electrode 203. The electricalisolation can be accomplished by disposing a silicon nitride or otherdielectric layer between posts 305 and diaphragm 303. Instead of using asilicon nitride layer, an undoped polysilicon layer can be deposited forposts 305 and diaphragm 303, and then a dopant can be controllablydiffused into diaphragm 303 but not substantially diffused into posts305.

Furthermore, FIG. 8 portrays an exposed portion of fixed electrode 203in cavity 401. However, in an alternative embodiment, isolation layer301 can cover all of the top surface of fixed electrode 203 to preventthe electrical shorting of diaphragm 303 and fixed electrode 203 asdiaphragm 303 moves toward fixed electrode 203 during the operation ofcomponent 100. Additionally, an extra isolation layer can be depositedafter the formation of sacrificial layer 202 and before the formation offixed electrode 203. This extra isolation layer prevents the electricalshorting of diaphragm 106 and fixed electrode 203 as diaphragm 106 movestoward fixed electrode 203 during the operation of component 100. Inthis alternative embodiment, fixed electrode 203 can be sandwichedbetween two isolation layers. In a different alternative embodiment,fixed electrode can remain exposed to cavity 401 while the bottomsurface of diaphragm 303 and the top surface of diaphragm 106 arecovered by different isolation layers.

Moreover, additional shielding structures can be incorporated intocomponent 100 to provide electrostatic shielding for component 100.Also, an electrical contact can be coupled to substrate 101 to provide afixed potential to substrate 101 for improved capacitance measurementaccuracy.

Accordingly, the disclosure of the present invention is not intended tobe limiting. Instead, the disclosure of the present invention isintended to be merely illustrative of the scope of the invention, whichis set forth in the following claims.

What is claimed is:
 1. A method of manufacturing a differentialcapacitor pressure sensor comprising:providing a semiconductor substratehaving first and second surfaces opposite each other; depositing a layerof a semiconductor material in physical contact with the second surfaceof the semiconductor substrate; forming a first movable diaphragm layeron the second surface of the semiconductor substrate wherein the firstmovable diaphragm layer forms a first electrode of the differentialcapacitor pressure sensor; forming a fixed electrode layer having afirst portion on the second surface of the semiconductor substrate and asecond portion overlying the first movable diaphragm layer wherein thefirst fixed electrode layer forms a second electrode of the differentialcapacitor pressure sensor; forming an isolation layer on the firstportion of the fixed electrode layer; forming a top movable diaphragmlayer having a first portion on the isolation layer and a second portionoverlying the second portion of the second portion of the fixedelectrode layer wherein the top movable diaphragm layer forms a thirdelectrode of the differential capacitor pressure sensor; and using anetchant to anisotropically etch a hole from the first surface of thesemiconductor substrate through the semiconductor substrate, toisotropically etch the layer, and to anisotropically etch the secondsurface of the semiconductor substrate wherein the hole at the first andsecond surfaces of the semiconductor substrate is larger than the holeat an inner portion of the semiconductor substrate and wherein theetchant is supplied to the second surface of the semiconductor substrateonly from the hole in the semiconductor substrate.
 2. The method ofclaim 1 further comprising forming the hole underneath the first movablediaphragm layer.
 3. The method of claim 2 wherein the forming stepoccurs before the using step.
 4. The method of claim 2 wherein theforming step includes forming a plurality of posts wherein the first andsecond movable diaphragm layers form a sealed cavity therebetween,wherein the fixed electrode layer and the plurality of posts are locatedin the sealed cavity, and wherein the plurality of posts mechanicallycouple the first and second movable diaphragm layers.
 5. The method ofclaim 1 wherein the providing step includes providing a semiconductorhaving a crystalline structure for the semiconductor substrate andwherein the depositing step includes providing the semiconductor havinga polycrystalline structure for the layer.
 6. The method of claim 1wherein using the etchant further comprises using the etchant to removethe layer wherein the etchant is supplied to the layer only from thehole in the semiconductor substrate.